The invention relates to a multilayer ceramic moulded part, limited by two virtually parallel surfaces and an edge, which internally contains one or more electrically conductive paths parallel to the two surfaces.
Such an object is known from U.S. Pat. No. 5,470,345 (HASSLER, B.A. et al.) Nov. 28, 1995. U.S. Pat. No. 5,470,345 describes a multilayer ceramic box consisting of several layers sintered onto one another, which layers contain electrically conductive paths on their surfaces. After these layers have been sintered, the ceramic wall of the box internally contains electrically conductive paths, virtually parallel to the surface. Electronic components and a battery are placed in the interior of the box, the wall of the box serving as a printed circuit board. The box, glued to with a lid, is then used for example as a pacemaker in the body.
A drawback of such a box is that it is made from ceramic layers formed from films cast from a suspension of a mixture of oxides and organic matter as described in HASSLE, BETH A. xe2x80x9cFast Turnaround Multilayer Coiled Ceramic Motherboard Fabricationxe2x80x9d. In: Proceedings of ASM""s 2nd Electronic Packaging: Materials and Processes Conference (October 1985): 117-121. This suspension was cast onto a carrier material, spread out to the required thickness with a doctor blade. The cast film was then carefully dried by passing air over it. The dried film was stored on a roll. The surface of the film thus prepared was provided with one or more electrically conductive paths. Several films were stacked on top of one another to obtain a multilayer object. Elimination of the organic binder through burning, and sintering then led to the formation of a multilayer ceramic moulded part that internally contained electrically conductive paths. A drawback of such a flexible film is however that it has an elongation at break which, in a composition of several layers, is insufficient for forming a curved surface without the film tearing in the outer layers or delamination occurring between the layers. A characteristic of the known multilayer moulded part is hence that it contains defects in the curvature. As a disadvantageous consequence of this, the electrically conductive paths created in the curved part of the moulded part are often interrupted.
The invention aims to provide a multilayer ceramic moulded part that does not present this drawback.
The multilayer ceramic moulded part according to the invention is characterised in that it is curved in at least one direction and is free of defects. Preferably the moulded part according to the invention is curved at an angle of 40xc2x0 to 180xc2x0, more preferably at an angle of 90xc2x0 to 180xc2x0. The moulded part according to the invention may have a radius of curvature at the curvature that is smaller than 100 mm and preferably smaller than 30 mm. Most preferably the radius of curvature of the moulded part according to the invention is smaller than 10 mm. In general, the radius of curvature of the moulded part according to the invention is greater than 1 mm and preferably greater than 3 mm. xe2x80x98Defectsxe2x80x99 are here and hereinafter understood to be delaminations between the layers and tears in the outer layers.
Preferably the moulded part is curved in two directions perpendicular to one another. This ensures that a closed moulded part consisting of only two parts, for example a box, can be composed.
If there are several conductive paths in a section through the thickness of the film, the distance between the conductive paths in a direction perpendicular to the surface of the moulded part is generally not critical and is determined by the minimum thickness of the film(s) of which the moulded part has been composed. As the minimum thickness of the film is approximately 1 xcexcm, the distance between the conductive paths in a direction perpendicular to the surface is greater than 1 xcexcm. It is difficult to indicate an upper limit to the distance between the conductive paths, as this will depend not only on the thickness of a single film, but also on the number of films stacked without a conductive path before another conductive path is applied. In general the aforementioned distance between the conductive paths will not exceed 100 xcexcm.
In addition to conductive paths parallel to the surface, the moulded part also contains conductive paths in a direction perpendicular to the surface. They will here and hereinafter be referred to as vias. They can be used to connect internal conductive paths with one another and with electronic components present on the surface of the moulded part, or to create electric passages through the wall of the ceramic moulded part.
Preferably conductive paths are at least in a curved part of the moulded part. This will ensure that optimum use is made of the surface of the curved moulded part to create passages and conductive paths parallel to the surface.
The invention also relates to process for the production of multilayer ceramic moulded part according to the invention.